Stihl 28, 38 Service Manual
F
SERVICE MANUAL
028/038
FOREWORD
This Service Manual covers model
028 chain saws up to machine
number
5561640
as well as later
machines unless technical information
bulletins have been issued
in
the meantime with updated
repair procedures.
Models
038
have substantially the
same constructional features as
model 028 chain saws" This Service
Manual can therefore be used
for the 038 chain saws as
well.
In
the event of faults it is quite pos-,
sible
that a single malfunction may
have several causes. It is, there-
fore,
advisable to consult the
"troubleshooting charts" when
tracing
faults"
We
also recommend
that you make use of the
exploded
views
in
the illustrated parts lists
while
carrying out repair work.
This service
manual and all techni-
cal information bulletins are
in-
tended exclusively for the use
of
STIHL servicing staff and dealers
and must not be passed on to third
parties.
STI
H
L®
Andreas Stihl
Postfach 1760
Repair
work
is made considerably
easier if the chain saw is mounted
on
assembly stand 59108503100.
The saw is
easily attached to the
stand by means
of
the two stud
bolts and collar
nuts
for bar mount-
ing"
While
on the assembly stand, the
chain saw can be
swivelled into any
required position to suit the repair
in
question" This not only has the
advantage of keeping the component
in
the best
position
for
the re-
pair, but
also leaves both hands
free for the work, and
thus
repre-
sents a considerable time-saving.
0-7050
Waiblingen
SPECIAL TOOL
MANUAL
1
Our
special tool manual illustrates
and lists the part numbers of all
available
machine-related tools as
well as general purpose tools for all
machines.
The
special tool manual is available
in various languages and can be
ordered
by
quoting the appropriate
part number
listed hereunder.
German
English
French
Spanish
Yugoslav
Swedish
Italian
Portuguese
0455
901
0023
04559010123
0455
901
0223
0455
901
0323
0455
901
0423
0455901 0523
0455
901
0723
0455
901
1223
p
2
CONTENTS
1 .
Specifications
4 4
..
Ignition System 26 4
.. 5 ..
1
Checking on breaker-
4.1
Construction 26
controlled ignition
45
4
..
2
Operation 26 4.5.2
Adjustment on
breaker-
2
..
Clutch, Chain Drive 4 .
.2
..
1
General information
26
controlled ignition
45
and Chain Brake
7
4.2.2
Breaker-controlled
4
.. 5 ..
3
Checking on
electronic
2.1
Construction magneto ignition 27 ignition
47
and operation
7
4 .
.2
..
3 Bosch
transistor-controlled
4.6 Magneto edge
gap
48
2
..
1.1
Clutch and chain sprocket 7
magneto ignition 28
2
..
1.2
Chain brake
8
4.2.4
SEM
thyristor-controlled
2.2
Troubleshooting chart
8
magneto ignition
29
2.3
Disassembly
and repair
9
4
..
2.4..1
Charging the storage 5
..
Rewind Starter
49
2
..
3.1
Clutch
9
capacitor
29
5
..
1
Construction
2.3
.
.2
Chain brake
12
4.2
..
4.2Triggering the
thyristor
29 and operation
49
2.4
Assembly
13
4 . .2.4..3 Ignition 30 5.2 Troubleshooting chart
49
2.4.1 Chain brake
13 4
..
3
Troubleshooting chart
31
5.3 Disassembly
50
2.4 .
.2
Clutch
14
4.3.1
Breaker-controlled
5.4 Replacing the
starter
ignition system
31
rope
50
4
..
3 .
.2
Electronic ignition
5.5
Replacing the rewind
3
..
Engine 15 system 32 spring
51
3.1
Construction 15 4.4 Function and repair 5
..
6 Tensioning the rewind
3.2 Troubleshooting chart
15
of components 33 spring
51
3
..
3 Exposing the
cylinder
16
4.4..1
Spark
plug
33
5.7
Replacing starter rope
3.4 Disassembly of cylinder 4.4..2 Ignition lead
34 guide bush
52
and piston 16
4
..
4.3
Short-circuit
wire/ground
5
..
8 Routine maintenance
52
3.5
Assembly
of piston wire 35
and
cylinder
17
4.4.4
Short-circuit
contact
36
3
..
6 Disassembly of crankcase 4.4.5 Flywheel
37
-
removal
of
crankshaft 19 4
..
4.6 Armature
(Bosch)/ignition
6
..
AV Handle System
53
3
.
.7
Installing the
Crankshaft
module (SEM)
39
6
..
1
Construction
-
assembly
of crankcase21 4.4..6
..
1 Resistance
test
on
and operation
53
3.8 Leakage testing
primary winding
39 6
.
.2
Repair
53
the
crankcase
23 4.4..6.2Resistance
test
on
3
..
8.1
Pressure test 23
secondary
winding
39
3
. .8.2 Vacuum
test
25
4.4..6
..
3 Ignition coil
tester
40
3.8
..
3
Replacing the oil seals 25 4.4..6.4 Disassembly 7
..
Master Control
55
and
assembly
40
7.1
Construction
4.4.7
Condenser
41
and operation
55
4.4.8
Contact
set
42
7
.
.2
Disassembly
4.4..9
Trigger plate
44
and
assembly
55
4
..
5 Ignition timing 44
8"
Electric Handle Heating
System
56
8,,1
Construction
and operation
56
8.2
Troubleshooting
56
8,,3
Disassembly
and assembly
58
8.3.1
Switch
58
8,,3,,2
Heating element
in pistol grip
58
8.3.3
Handlebar
58
8,,3..4
Generator
59
9"
Chain Lubrication
60
9.1
Construction and
operation of oil pump
60
9,,2
Troubleshooting chart
61
9,,3
Oil
tank/tank
vent
62
9..4
Repair
of
pickup body
and valve
62
9.5
Disassembly and repair
of
oil pump
63
1O"
Fuel System
64
1
0,,1
Construction and
operation
of
carburetor
64
10"1,, 1 Operation of fuel pump
64
1 0.1,.2 Operation of carburetor
64
10,,2
10,,3
10..4
10.5
10,,6
10,,6,,1
Troubleshooting chart
66
Leakage test
on carburetor
68
Disassembly
of
carburetor
68
Repair
of
carburetor
69
Carburetor adjustment
71
Notes for fine adjustment
of
carburetor
71
3
10.7
Fuel line and tank vent
71
10.8
Air filter and choke
72
4
1. SPECIFICATIONS
1.1
Engine
1.2
Fuel System
STIHL single cylinder, two-stroke engine with special impregnated
cylinder bore
Displacement:
Bore:.
Stroke:
Compression
ratio::
Max. torque:
Max.
permissable engine speed:
Mean
idle speed:
Crankshaft:
Crankshaft bearings:
Crankpin:
Big-end bearing:
Piston pin:
Small-end bearing:
Rewind starter:
Starter rope:
Clutch:
Clutch
engages at:
Crankcase
leakage test:
with overpressure::
with vacu u
m:
Carburetor:
Adjustment:
high-speed adjustment screw
H:
low-speed adjustment screw
L:
Carburetor leakage test
with overpressure:
Fuel capacity:
47 cm3 (2
..
87 tu. in)
44
mm
(1.73 in)
31
mm
(1.22 in)
9.5:1
2
..
65
Nm
(1..95
Ibf. ft) at
6000
rpm
12000
rpm
2200
rpm
Two-part, drop-forged
2 deep-groove ball bearings
14..4
mm
(0.57 in) dia.
Needle cage
10
..
0
mm
(0
..
39 in) dia.
Needle
cage
Pawl engagement with automatic
starter rope rewind mechanism
3.5
mm
(0
..
14
in) dia.,
1060
mm
(41.8 in) long
Centrifugal
clutch without linings,
76
mm
(3
in) dia.
Approx.
3100 rpm
po
= 0
..
5 bar
(7
..
1 Ibf/in2)
pu
= 0.5 bar
(7.1
Ibflin2)
All-position
diaphragm
carburetor with
integral
fuel
pump
Open approx.
11/4
turns
Open approx
..
1114
turns
(basic setting with screws
initially
hard against their seats)
po
= 0.4 bar
(5
..
7 Ibflin2)
0.52 L
(1..1
U.S.pt)
1.3
Ignition System
Fuel mixture:
Air
filter::
028
AV
and
028
AVQ
Type:
Magneto edge gap:
Air gap:
Ignition timing:
Ignition advance angle:
Breaker point
gap::
Condenser:
Armature:
028
AVE
Type:
Air gap:
Ignition timing::
Ignition advance angle:
Armature:
028
AVEQ
Type:
Air gap:
Ignition timing:
All Models
Spark plug (suppressed):
Spark
plug thread:
Fuel mix 1 :40 with
STIHL two-cycle engine oil;
1 :25 for other branded
two-cycle engine oils
Flat
wire mesh filter
Breaker-controlled magneto
ignition system
4
..
" 8
mm
(0,,16
. " .
0.31
in)
0,,2
...
0.3
mm
(0.008" " .
0.012
in)
2.2
..
,,2,,3
mm
(0.087" ,
,,0.091
in)
before
T..D"C.
27"".28°
5
0.35
...
0.4
mm
(0.014. , .0.016 in)
Capacitance
0.15" " .
0.19
IlF
Coil
resistors
Primary
0..7
...
1,,00
Secondary
7..7
...
10.3
kQ
Transistor-controlled (breaker-
less) magneto ignition system
0.2.
" .
0,,3
mm
(0,,008,. ,
0.012
in)
2.6
mm
(0,,1
in) before
T.D.C"
at 8000 rpm
30° at 8000 rpm
as
028 AV/028
AVQ
Thyristor-controlled (breaker-
less) magneto ignition system
0,,2
...
0.3
mm
(0.008
...
0,,012
in)
2.6
mm
(0,,1
in) before
T.D.C"
at 8000 rpm
Bosch
WSR
6 F
or
Champion
RCJ
6 Y
Heat range: 200
Electrode
gap::
0.5
mm
(0,,02
in)
M 14x1..25; 9.5
mm
(0.37
in)
long
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